Assessment (as of 31 August 2018):
- In the past month or so, sea surface temperatures of the central and eastern equatorial Pacific continued to warm and were still within the normal range. Based on the latest oceanic observations as well as forecasts by a number of climate models around the world, the warming trend is expected to continue in the next few months. The development of El Niño is likely to start in autumn (September - November) 2018. During El Niño, the chance of normal to above-normal temperature in Hong Kong in autumn is higher while the chance of normal to below-normal rainfall in Hong Kong in autumn is slightly higher.
- Under the influence of global warming and local urbanization, autumn temperatures in Hong Kong exhibit a significant long-term rising trend. The chance of normal to above-normal temperature is generally higher. This temperature trend is in line with the autumn temperature forecast for southern China given by climate models around the world.
- Climate models around the world generally forecast that the moisture transported to the south China coast this autumn is likely to be less than normal. Under this situation, autumn rainfall in Hong Kong in 2018 is likely to be normal to below normal.
- Climate prediction centres around the world generate seasonal forecasts, employing a variety of methods including
dynamical models, statistical methods, expert judgment and combinations of them. Predictions from different centres do
not always agree and large discrepancies can occur at times. The Observatory adopts an ensemble approach to formulate
its seasonal forecast for Hong Kong, taking into consideration available products from major climate prediction centres
and the Global-Regional Climate Model (G-RCM) operated in house. Thus,
the resulting forecast issued by the Observatory may be different from the forecast given by G-RCM.
- The Observatory gratefully acknowledges the Tokyo Climate Center of the Japan Meteorological Agency and the National
Centers for Environmental Prediction of National Oceanic and Atmospheric Administration, USA for providing dynamical
prediction model forecast and hindcast data to support the formulation of seasonal forecast for Hong Kong.
- Forecast for winter 2018 (December 2018 to February 2019) will be available around 1st December 2018.
Seasonal forecast charts provided by G-RCM and major climate centres: